The present application relates to electronic lighting. More specifically, it relates to a dimmable electronic ballast and will be described with particular reference thereto. It is to be appreciated that the present ballast can also be used in other lighting applications, and is not limited to the aforementioned application.
In the past, dimmable ballast systems have typically been composed of multiple discrete ballasts. In order to achieve a lower light output, one or more of the ballasts would be shut off. Conversely, when greater light output is desired, more ballasts are activated. This approach has the drawback of only being able to produce discrete levels of light output. With each ballast only able to produce a single light output, the aggregate output is limited to what the various combinations of the ballasts present can produce. Moreover, this setup also requires multiple lamps for the same space to be lighted, resulting in an inefficient use of space.
Another approach in dimmable lighting applications has been to dim a single ballast by varying the operating voltage of the ballast, that is, by varying the voltage of the high frequency signal used to power the lamp. One drawback in such a system is that as the voltage of the high frequency signal is diminished, the lamp cathodes cool down. This can lead to the lamp extinguishing, and unnecessary damage to the cathodes. To avoid this problem, such systems apply an external cathode heating. While this solves the problem of premature extinguishing, the ballast is drawing power that is not being used to power the lamp. This decreases the overall efficiency of the ballast.
The present application contemplates a new and improved dimmable electronic ballast that overcomes the above-referenced problems and others.